https://0xacab.org/monkeysphere/monkeysign/issues/50 shows how a programmatic
user of GnuPG struggled with the silent deprecation of --secret-keyring.
If this option is actually deprecated, there should probably be a warning so
folks know to stop using it.
The developer on that bug report ended up resolving his issues by setting up
symlinks to the standard gpg-agent socket, aiui. If this is the preferred
mechanism, maybe it should also be documented?